This invention relates to sprayers having rotary atomizers and has particular, though not exclusive, application to agricultural crop-spraying equipment.
Liquid sprays are applied to crops and agricultural land for a variety of reasons but a principal use is for the application of pesticides, which may be herbicides, insecticides or fungicides. For efficient use of these relatively costly materials it is important that the droplets in the spray are of a size suitable for the application and ideally the droplets should be of uniform size.
The significance of control of droplet size is that, if they are too large they will not provide even coverage over foliage or other surfaces to be sprayed and they will also fall to the ground too quickly. Also an excessive quantity of liquid tends to be expanded. On the other hand if the droplet size is too small, the droplets will be too easily carried on the wind and again even distribution on the surface to be sprayed is impaired. There is therefore an optimum range whereby even distribution and minimum liquid material consumption is obtained this being usually in the range of 20-500 microns in diameter.
Conventional pressure atomizer sprayers are not capable of giving small, uniform size droplets, so rotary atomizers having discs or hollow cones are preferred. Liquid is fed to the centre of the atomizer disc or cone and rotation results in migration of the liquid to the periphery from which it is discharged as a series of droplets. The atomizer disc or cone advantageously has a serrated perimeter so that the liquid is dicharged from a series of points of small dimensions and there may be radial grooves to feed the liquid to these points. Such a design is based on the observation that the best results in terms of droplet size and uniformity, are obtained if the liquid issues from the points as discrete filaments which are broken up into droplets after leaving the atomizer.
In order to obtain even spray distribution from a rotary atomizer it is necessary to supply liquid to the rotary part disc or cone in such a manner that the distribution around the periphery, from which the liquid leaves the atomizer, is an uniform as possible. One arragement is to provide a hollow shaft through which the liquid is discharged through a radial opening onto the adjacent rotating surface of the rotary part, but thhis can lead to uneven supply to the inner portion of the rotary part and therefore similarly uneven distribution at the periphery.